1. Field of the Invention
The present invention relates to a driver circuit, associated drive control method and an image reading apparatus. More particularly, the present invention relates to an image reading driver circuit and its drive control method as well as an image reading apparatus comprising this driver circuit in which a plurality of detection signals corresponding to a detectable object image pattern are read out in parallel and output as time series read data.
2. Description of the Related Art
Conventionally, there are image reading apparatus for reading detectable object images contained in printed material, photographs, fingerprints, etc., for example, a CCD (Charged Coupled Device) which includes a photosensor array comprising a plurality of photosensors (photoelectric transducers) arrayed in a line form (one-dimensional) or a matrix form (two-dimensional) A known configuration exposes irradiated light toward a read object (detectable object) placed upon the detection surface of a photosensor array. The reflected light of the read object is sequentially scanned for every row and read. The electrical signals (detection signals) detected corresponding to a detectable object image pattern of each of the photosensors for every column is read out in parallel. Subsequently, parallel-to-serial conversion is performed and the read data containing time series data is generated and outputted.
FIG. 16 is an outline configuration diagram showing one example of a conventional prior art image reading apparatus.
FIG. 17 is an outline configuration diagram showing another example of a conventional prior art image reading apparatus.
In the example shown in FIG. 16, the outline configuration comprises a photosensor array 110Y containing a plurality of photosensors PSy comprised of photodiodes PD arrayed in a matrix form; a scanning driver circuit 120Y for sequentially setting in a selective state and scanning the photosensors PSy for every row; a signal driver circuit 130Y for receiving in parallel the detection signals outputted from the photosensors PSy of the rows being set in a selective state and outputting the read data Vdata containing time series data; and a timing control circuit 140Y for supplying a predetermined timing control signal to the scanning driver circuit 120Y and the signal driver circuit 130Y as well as for controlling the image reading operation of a detectable object image.
Here, the signal driver circuit 130Y, for example, has a configuration comprising a storage capacitor Cy (may be wiring capacity which is parasitic on the read-out lines Lread) for receiving in parallel and maintaining for every column (read-out lines Lread) the electrical signals (detection signals; for example, voltage corresponding to a photoelectric charge) detected corresponding to the detectable object image pattern by the photosensors PSy of the rows being set in a selective state by the scanning driver circuit 120Y; an amplifier AMPy for amplifying the voltage components of the detection signals maintained in the storage capacitor Cy for every column to a predetermined voltage level; and a multiplexer MPL for performing parallel-to-serial conversion of the amplified processed detection signals and generating output of the read data Vdata containing of time series data.
Moreover, as seen in FIG. 17, the outline configuration comprises a photosensor array 110Z consisting of a plurality of photosensors PSz comprising phototransistors PT in a one dimensional array; and a signal driver circuit 130Z for receiving in parallel the detection signals detected by each of the photosensors PSz and outputting the read data Vdata containing time series data.
Here, the signal driver circuit 130Z, for example, has a configuration comprising a storage capacitor Cz (may be wiring capacity which is parasitic on the read-out lines Lread) for receiving in parallel and maintaining the electrical signals (detection signals) detected by each of the photosensors PSz corresponding to a detectable object image pattern; a shift register SRz for sequentially outputting at predetermined timing the shift signals Sp1, Sp2, Sp3 . . . corresponding to each of the photosensors PSz; a transistor group TRG (switches) for outputting in time series the detection signals maintained in the storage capacitor Cz for each of the above-mentioned photosensors PSz as “ON” operations are sequentially performed based on the shift signals Sp1, Sp2, Sp3, . . . and a single amplifier AMPz for amplifying the voltage components of the detection signals outputted in time series to a predetermined voltage level and outputting as the read data Vdata.
Thus, either configuration of the image reading apparatus disclosed in conventional prior art has a structure in which an amplifier is provided for amplifying the detection signals (electrical signals) detected by photosensors to a predetermined signal level. For that reason, there are drawbacks as described below.
Specifically, as seen in FIG. 16, in the case of having a configuration provided with a plurality of amplifiers corresponding to each of the photosensors for amplifying individually and in parallel the detection signals outputted from the photosensors of every column, a plurality of the above-mentioned amplifiers are constantly set in a drive state during an image reading operation period which reads a detectable object image. Thus, because electrical current is constantly supplied based on bias voltage for this drive, there are drawbacks in that this configuration generates an increase in power consumption in the image reading apparatus and increases the amount of heat generation in the read-driver circuit.
Furthermore, as seen in FIG. 17, there is the case of having a configuration which performs amplification processing using a single amplifier after parallel-to-serial conversion of the detection signals outputted from each of the photosensors. Although the installed number of amplifiers and associated installation areas can be reduced, in order to perform essential amplification processing of the detection signals (read data) after conversion to time series data and to sequentially correspond with that time series timing, the drive frequency of the amplifier must be set higher. Thus, this configuration also has the drawback of generating an increase in power consumption.